In the field of electro-optics, solid state devices are being developed to improve existing apparatus and make possible functional achievements never before attainable. That is especially true in the field of integrated optics wherein the present invention resides.
Some materials are transmissive to some wavelengths but are absorptive of shorter wavelengths. The shift of the optical absorption edge to lower energies (longer wavelengths) under the influence of an electric field has been predicted for insulators and semiconductors by Keldysh and Franz in 1958. Their predictions along with the experimental observations of Williams, Moss, and Boer et al, and Vavilov and Britsyn opened up a new branch of physics which has since grown and ramified. The potential use the Franz-Keldysh effect as a mechanism for intensity light modulation has also been recognized by the early workers in the field of electro-optics. But, the nonlinearity of the effect coupled with difficulties in the materials limited the use of these devices. Recent development in material technology in the field of integrated optics has spawned new techniques and attempts at devising new electroabsorption light modulators, switches and detectors.
The invention of the above-identified, related U.S. Pat. application is directed to the Franz-Keldysh mechanism in materials as they apply to electroabsorption, light modulation and detection. The geometry of the embodiment described consists of a liquid phase epitaxy GaAs double-heterojunction structure. Depending on the application, light is either coupled parallel to the junction or transmitted perpendicular to it. The former would be used as a component in integrated optics whereas the latter would find other applications. In the latter the GaAs substrate and top electrode could be removed by etching. In both cases, a reverse bias to the device will generate a high electric field within the GaAs material and induce a shift of its optical absorpton edge to lower energies. Light having photon energy slightly less than the level of the absorption edge will be attenuated in the GaAs region, and electron hole pairs will be created and swept out into the electrical contact in the presence of a high electric field. The latter phenomenon is photodetection and can be used as a means of detecting the light. Thus, a train of light pulses can be either transmitted through the device by applying no electric field to the active region or attenuated by applying a reverse bias. At the same time the light's presence can be detected through photodetection when a large field is applied, i.e., electroabsorption.
The present invention utilizes the invention of the above-identified related application in a data bus coupler wherein multiple channels of information are conveyed by a single conveyence means such as a fiber optics bundle, and the channels are separated into a plurality of separate channels each of which includes a modulator or detector device. Each modulator or detector can then independently process or detect selected portions of the information determined by the electric field applied. After modulation the channels may be recombined into a bundle for further conveyance and detected at a further point down the fiber. The modulators are in parallel, but the detectors may act in series or in parallel as desired.